The formation of round bodies by the anaerobic, Gram-negative streptobacillus used in the S-F medium under the influence of penicillin G has been reported.
Actively propagating E. histolytica trophozoites ingest the round bodies roughly in proportion to the numbers available.
Streptobacillus variants that do not support propagation of E. histolytica do not produce the round bodies. There is a rough parallel between round body production and ability to support propagation of E. histolytica in six variants studied.
Normal horse serum and glucose do not influence the production of the round bodies.
Those variants not producing round bodies in the presence of penicillin G are somewhat more resistant to the antibiotic than are those which produce round bodies.